Linux Magazine has a profile of Daniel Fore and the Elementary project. Elementary is a Linux distro that's committed to a clean and simple user experience, but it's more than a distro - it's actually a multi-pronged effort to make improvements to the user experience for a whole ecosystem of components, including icons, a GTK theme, Midori improvements, Nautilus, and even Firefox. The work that elementary is doing isn't limited to their own distro, and some of their work is available in current, and perhaps future, Ubuntu releases. The results are really striking, and I think it's probably the handsomest Linux UI I've ever seen.

Funny that you mention Autocad, AFAIK there's no OS X version for it either, so in your argumentation OS X isn't a ready for the desktop either. Or exchange again, no OS X version. As a side node, I would argue that the number users who use windows because of Autocad is probably as big as the number of users who use Linux because of Gnome. Autocad is really not a consumer product, and to say otherwise is simple dishonest. That said if you have to run Autocad for work, it is probably a valid reason for using Windows (at least in a VM). About exchange, there are many Groupware suites around which provide the same functionality, but it's funny that you bring exchange up in a discussion about the Desktop, as it is a server application.